The development of the laser in 1960 opened the possibility of the application of this form of energy in a number of medical disciplines. Lasers offer the advantages of high power, narrow spectral widths, small focused spot sizes, and good absorption of the energy by the target tissues. Since then, numerous lasers of different wavelengths and modes of operation have been developed, and many of these have been used in specific medical applications. For example, the argon laser, with emission in the blue-green part of the visible portion of the electromagnetic spectrum, has found extensive use in ophthalmology because of its good transmission by the ocular media and good absorption by the target tissues in the retina and choroid.
Among the many lasers that have been developed, however, the carbon dioxide laser, with its emission wavelength of 10.6 microns, offers the most extensive range of applications in medicine because it is highly absorbed by all tissues of the body. For this reason, by focusing the carbon dioxide laser on tissues, it is possible to photocoagulate, to cut, or to vaporize almost any tissue of the body. The carbon dioxide laser has been applied to a number of medical problems in various disciplines--including otolaryngology, gynecology, neurology, dermatology, and in plastic and general surgery.
In the field of gynecology, the carbon dioxide laser has been used almost exclusively for medical intervention in a number of disorders. The laser is used for making incisions, to coagulate small arteries and veins, and to vaporize tumors and other abnormal tissues.
A number of instruments have been developed for use in the field of gynecology. These devices typically comprise a console that contains the power supplies, vacuum pump, gas tanks, and water pump and heat exchanger, for operating the laser. An umbilical cord is typically used to connect the console with a laser head that is directly coupled to a colposcope or an operating microscope, supported by a stand that is free standing or is connected to the console. The operating microscope is typically mounted on an optical head assembly which may be provided with a micromanipulator--more popularly, a joy-stick--to permit the operating physician free control of the locus of impact of the beam on the target site.
In such laser systems, the laser energy is produced in a laser head and is transmitted to the target site by a series of redirecting mirrors. The last mirror in the path is linked mechanically to the joy-stick to permit the desired manipulation. To permit the desired movement of the beam on a target plane separated a specified distance such as, for example, a foot from the viewing optics of the operating microscope, the mechanical linkage between the micromanipulator and the last mirror must provide for two degrees of freedom, conveniently referred to as the x and y axis. A problem arises, however, in linking the micromanipulator to the last mirror. If the axis of rotation of the mirror is normal to the plane of the incident and reflected laser beam, then each degree of rotation of the mirror results in a two degree change in the direction of the deflected beam (y axis); however, if the rotation of the mirror is about an axis lying within the plane of travel of the beam, then each degree of mirror rotation is matched by one degree of beam deflection (x axis). Thus, direct linkage of the micromanipulator to this last mirror without compensation results in a distortion in one dimension so that if the micromanipulator were to trace a circle, the deflection of the laser beam by the mirror would trace an ellipse whose minor axis corresponded to the radius of the circle.